Several improvements in sequencer chemistry and supports have facilitated primary structure determination of two cyclic nucleotide phosphodiesterase, including identification of the cGMP binding site of one of the enzymes, a hormonally-regulated phosphoprotein associated with the adipocyte fat droplet, a protein specifically expressed in regenerating optic nerve, a novel bone morphogenetic protein isolated from mammalian cartilage, adhesion molecules from two oral pathogens, the nucleotide binding site of human platelet glycoprotein IIb, the Dictyostelium homolog of the GroEL protein, and a heretofore undescribed calmodulin binding protein from mammalian brain. Subpicomol determinations are now routine; we have recently obtained the majority of a protein's primary structure from a few microbrams of electrophoretically-separated material in one of the cases mentioned above. These procedures open the door to analysis of low- abundance polypeptides; further work will be directed toward identification and structure determination of additional proteins important in biological signal transduction.